Great game and really fun, though obviously being in alpha there are plenty of problems to iron out and most likely a lot more content coming eventually. As an up-and-coming gamedev myself, I understand how much work this project likely is. That being said, I do have a few suggestions that it'd be nice to see you implement as long as it's not too hard:
-More bosses (2-4 per floor, maybe even 5, probably following the same design schemes as current bosses (similar to regular Isaac bosses but different))
-Some sort of proper boss splash intro screen
-Maybe another floor or floor variants of some sort
-Minibosses (harder enemies that have a small chance of spawning, only one per level or possibly per floor, could be the sins or horsemen or something else)
Once again, while these would be great to see, I know how painful the development process can be so don't feel too pressured!